The breakdown voltage of a semiconductor device is significantly affected by the electric field distribution within and near the device. Accordingly, methods of increasing device breakdown voltage by altering or controlling the electric field distribution have been extensively developed in the art, and are often referred to as field shaping methods. Structures employed for field shaping include guard rings, floating field plates, and biased charge control electrodes.
For example, in U.S. Pat. No. 6,190,948, field shaping between an active region of a device and floating field ring around the device is provided by several overlapping floating field plates between the active region and the field ring. The overlap of the field plates increases the capacitive coupling between the plates. In this example, field shaping is provided in a termination region of the device.
Field shaping has also been employed within devices (e.g., between the source and drain of a field effect transistor (FET)) to increase breakdown voltage. For example, in U.S. Pat. No. 6,717,230, biased charge control electrodes in a drift region of a FET are employed to provide field shaping within the drift region. In U.S. Pat. No. 6,110,804, floating field conductors are disposed above the top surface of a FET drift region to provide field shaping at the surface of the drift region. Charge is injected onto the floating field conductors (e.g., by biasing the device into breakdown) such that a depletion region is formed in the drift region.
However, these examples of known field shaping approaches also provide examples of undesirable complications that can arise in practice. For example, fabrication of overlapping field plates as in U.S. Pat. No. 6,190,948 can be relatively complicated. Individual biasing of charge control electrodes as in U.S. Pat. No. 6,717,230 can be complicated to implement in practice. In U.S. Pat. No. 6,110,804, the injection of charge onto the floating field conductors can generate practical issues, such as providing the proper amount of injected charge, and dealing with leakage of the injected charge over time.
Accordingly, it would be an advance in the art to provide field shaping having improved performance with structures that can be provided by relatively simple fabrication methods.